Laser-induced Forward Transfer Research Articles

Elucidating the transfer dynamics of high-viscosity silver paste for laser-induced forward transfer of continuous line

Laser-induced forward transfer (LIFT), as an innovative 3D direct-write method, has been increasingly applied for various material printing in many applications. Elucidating the transfer process of paste is crucial to manipulate the printing quality. In this work, the transfer dynamics of high-viscosity silver paste in LIFT of continuous line was systematically investigated based on the cumulative effect from images obtained over hundreds of laser pulses. The influences of process parameters, including the laser energy input (single pulse energy, repetition frequency, and scanning speed) and the thickness of paste film, on the bump height and expansion velocity of bump front were analyzed. With increasing the single pulse energy or repetition frequency, or decreasing the scanning speed or film thickness, the evolution of bump morphology and sputtering varies from just a tiny bump with no sputtering, to a moderate-sized bump with a small amount of sputtering and rebounding, and further to a large bump with intense sputtering and rebounding. A non-dimensional group in terms of Reynolds and Weber numbers was proposed to categorize different evolution regimes and claim the physical mechanism on LIFT of continuous line. When the Reynolds number is greater than 0.01 and the Weber number is greater than 0.1, the inertial effect is sufficient to resist the viscous and capillary effects, inducing the paste to bulge and transfer downwards. A moderate-sized bump with no visibly fragmented sputtering is desirable for the transfer of continuous grid lines. The forming status of grid lines can be predicted according to the behavior of paste transfer, and the predicted grid line state agrees well with the actual state. This can provide process and theoretical references for printing continuous grid lines with LIFT.

Preparation of brittle ITO microstructures using Laser-Induced forward transfer technology

The performance of transparent conductive microstructures plays a significant role in determining the device efficiency. The fabrication of ITO microstructures on the flexible optoelectronic devices remains challenging because of the high-temperature processing requirements and brittleness of the ceramic material. This paper highlights a three-dimensional microfabrication technique that combines sacrificial layer etching and laser-induced transfer. By studying the donor material thickness and the laser energy density, control of the sacrificial layer transfer thrust was achieved to yield an optimal microstructure performance. Different shapes of ITO transparent conductive microstructures were fabricated on polydimethylsiloxane (PDMS) surfaces, demonstrating structural integrity, visible light transmittances > 90 %, and resistivities of ≤ 8 × 10−4 Ω·cm. Finite element analysis was employed to simulate the impact transfer of the donor material onto the receiving substrate, thereby elucidating the energy-absorbing protective role of the flexible PDMS layer. Effective control of the transfer force was identified as a crucial factor in achieving the successful transfer of brittle films. This high-precision and rapid array processing approach meets the demands of automated batch manufacturing, indicating its potential for use in patterned processing on flexible substrates, as an alternative to lithographic techniques. This technique could be applied in the preparation of electronic skins and flexible devices. Additionally, for the first time, a 3 × 3 pixel resistive array sensor was integrated on a Ag nanowires/PDMS surface, demonstrating array pressure-sensing capabilities at pressures of 0–80 kPa. This study represents a significant step towards the development of multifunctional flexible optoelectronic devices.

Preparation of brittle ITO microstructures using Laser-Induced forward transfer technology

The performance of transparent conductive microstructures plays a significant role in determining the device efficiency. The fabrication of ITO microstructures on the flexible optoelectronic devices remains challenging because of the high-temperature processing requirements and brittleness of the ceramic material. This paper highlights a three-dimensional microfabrication technique that combines sacrificial layer etching and laser-induced transfer. By studying the donor material thickness and the laser energy density, control of the sacrificial layer transfer thrust was achieved to yield an optimal microstructure performance. Different shapes of ITO transparent conductive microstructures were fabricated on polydimethylsiloxane (PDMS) surfaces, demonstrating structural integrity, visible light transmittances > 90 %, and resistivities of ≤ 8 × 10−4 Ω·cm. Finite element analysis was employed to simulate the impact transfer of the donor material onto the receiving substrate, thereby elucidating the energy-absorbing protective role of the flexible PDMS layer. Effective control of the transfer force was identified as a crucial factor in achieving the successful transfer of brittle films. This high-precision and rapid array processing approach meets the demands of automated batch manufacturing, indicating its potential for use in patterned processing on flexible substrates, as an alternative to lithographic techniques. This technique could be applied in the preparation of electronic skins and flexible devices. Additionally, for the first time, a 3 × 3 pixel resistive array sensor was integrated on a Ag nanowires/PDMS surface, demonstrating array pressure-sensing capabilities at pressures of 0–80 kPa. This study represents a significant step towards the development of multifunctional flexible optoelectronic devices.

Thermal simulation of laser-induced forward transfer for Au donor film

Thermal simulation of laser-induced forward transfer for Au donor film

Precision isolation and cultivation of single cells by vortex and flat-top laser ejection.

Single-cell isolation stands as a critical step in single-cell studies, and single-cell ejection technology based on laser induced forward transfer technology (LIFT) is considered one of the most promising methods in this regard for its ability of visible isolating single cell from complex samples. In this study, we improve the LIFT technology and introduce optical vortex laser-induced forward transfer (OV-LIFT) and flat-top laser-induced forward transfer (FT-LIFT) by utilizing spatial light modulator (SLM), aiming to enhance the precision of single-cell sorting and the cell's viability after ejection. Experimental results demonstrate that applying vortex and flat-top beams during the sorting and collection process enables precise retrieval of single cells within diameter ranges of 50 μm and 100 μm, respectively. The recovery rates of Saccharomyces cerevisiae and Escherichia coli DH5α single cell ejected by vortex beam are 89 and 78%, by flat-top beam are 85 and 57%. When employing Gaussian beam sorting, the receiving range extends to 400 μm, with cultivation success rates of S. cerevisiae and E. coli DH5α single cell are 48 and 19%, respectively. This marks the first application of different mode beams in the ejection and cultivation of single cells, providing a novel and effective approach for the precise isolation and improving the viability of single cells.

Application of Conductive Coatings on a Flexible Polymer Substrate via Laser-Induced Forward Transfer

Application of Conductive Coatings on a Flexible Polymer Substrate via Laser-Induced Forward Transfer

High-definition direct-print of metallic microdots with optical vortex induced forward transfer

We demonstrate high-definition, direct-printing of micron-scale metallic dots, comprised of close-packed gold nanoparticles, by utilizing the optical vortex laser-induced forward transfer technique. We observe that the spin angular momentum of the optical vortex, associated with circular polarization, assists in the close-packing of the gold nanoparticles within the printed dots. The printed dots exhibit excellent electrical conductivity without any additional sintering processes. This technique of applying optical vortex laser-induced forward transfer to metallic dots is an innovative approach to metal printing, which does not require additional sintering. It also serves to highlight new insights into light–matter interactions.

Effect of laser bioprinting on growth characteristics of yeasts

Laser-induced forward transfer (LIFT) can be helpful for bioprinting of microbial cells, but data on its impact on the microbial physiology are scarce. The aim of study was to investigate the LIFT effect on eukaryotic microorganisms (yeasts) growth characteristics. Candida albicans, Lipomyces lipofer and Saitozyma podzolica yeasts were printed on solid and liquid nutrient media and compared with traditional methods of inoculation. The laser bioprinting affects growth patterns of yeasts, leading to formation of subpopulations with different growth characteristics. The data obtained highlight necessity of studies of the LIFT effect on microorganisms’ physiology.

Alternate deposition and remelting microdroplets via single laser for printing low-defect and high-performance metal micropillars

Laser-induced forward transfer (LIFT) has emerged as a versatile technique for printing high-resolution metal microstructures. However, a common drawback of this method is the inadequate coalescence of the deposited metal microdroplets, which results in inferior electrical and mechanical properties. This paper proposes a novel approach for fabricating high-performance metal micropillars using a single-pulsed laser to alternately deposit and remelt metal microdroplets. Specifically, an ultraviolet nanosecond laser was used to induce the deposition of copper microdroplets, forming a patterned powder bed with high resolution. Subsequently, a laser pulse train was applied to fuse the patterned powder bed. The results showed that voids and microdroplet delamination were eliminated in the printed copper micropillars, whose yield strength and elastic modulus increased threefold, approaching 63% of those of the bulk metal. The remelting behavior of the deposited microdroplets was elucidated by modelling and analysing the thermal accumulation effects of a laser pulse train. A remelting map was proposed, including the non-melting, remelting, and vaporizing regimes. According to the depth of melt pool, the evolutions of morphology and microstructure in the depositing and remelting process were elucidated. Hence, this study advances the LIFT process for fabricating high-performance metal microstructures.

Lithography‐free fabrication of a local contact interlayer for Si‐based tandem solar cells

AbstractCurrently, the Si solar cell market share is dominated by PERC solar cells. Although the efficiency of PERC solar cells has been steadily increasing, it is expected to reach the practical efficiency limit in the near future. The thin film/PERC Si tandem cell technique can be one of the solutions to overcome the single‐cell efficiency limit. In this study, we developed a novel interlayer fabrication technology for the diffused junction Si solar cells of the PERC and Al BSF cell architectures. We combined laser contact opening (LCO) and laser‐induced forward transfer (LIFT) processes to fabricate local contact opening with low contact resistance while maintaining the high passivation performance of the Si bottom cell. The dielectric‐passivated emitter of the Si solar cell was ablated locally by the LCO process, and subsequently, the Ti nanoparticles were transferred selectively by the LIFT process to the opened emitter region followed by transparent conducting oxide deposition. Laser process parameters were carefully optimized to fabricate low‐loss interlayers. We applied the developed interlayer fabrication technology to the Si bottom cells of Al BSF and PERC cells. Finally, we demonstrated successfully the perovskite/PERC Si tandem cell with an interlayer developed in this study. The developed interlayer fabrication technology does not include a photolithography step and vacuum deposition processes for buffer metals; thus, we expect it may be more compatible with the mass production of thin film/diffused junction Si tandem solar cells.

One-Step Non-Contact Additive LIFT Printing of Silver Interconnectors for Flexible Printed Circuits

The single-pass one-step method for printing conductive silver tracks on a glass surface, using the laser-induced forward transfer (LIFT) technique, was proposed, providing a unique opportunity for high-throughput printing of surface micro- and nanostructures with high electrical conductivity and positioning accuracy. This method was developed via our multi-parametric research, resulting in the selection of the optimal material, laser irradiation, and transfer conditions. Optical, scanning and transmission electron, and atomic force microscopy methods, as well as X-ray diffraction, were used to characterize the surface structure and phase state of the printed structures, while energy-dispersive X-ray and X-ray photoelectron microscopy were employed for their chemical microanalysis. Depending on the laser irradiation parameters, the specific electrical conductivity of the printed tracks varied from 0.18 to 83 kS/cm, approaching that of donor magnetron-sputtered films. This single-pass one-step method significantly facilitates fast, large-scale, on-demand local laser printing of metallic (sub)microcomponents of microelectronic devices.

One-step additive LIFT printing of conductive elements

The feasibility of printing silver and copper conductive elements on a glass substrate in a one- step through the laser-induced forward transfer method has been successfully demonstrated. The topography of the resulting elements was analyzed, using scanning electron microscopy. Investigation of their chemical composition was conducted by means of energy-dispersive x-ray spectroscopy and x-ray diffraction, revealing that both silver and copper in their metallic nanocrystalline state. The maximum specific conductivity of ≈6 kS cm−1 was achieved for both silver and copper at the optimal scanning speed of 3800 mm s−1, providing two-pulse printing with the laser transfer by the first pulse and laser annealing by the second one. The proposed method facilitates the technological additive printing process of conductive elements and rises its throughput.

A review on critical challenges in additive manufacturing via laser-induced forward transfer

A review on critical challenges in additive manufacturing via laser-induced forward transfer

The Basic Concept and Application Status of Laser Induced Forward Transfer

Laser Induced Forward Transfer (LIFT) is a new type of transfer method. It uses high-energy laser as an energy source to irradiate solid or liquid materials, allowing them to be emitted onto the receiving substrate under the force of steam to achieve the transfer of material. Nowadays, although most of the work on LIFT is still in the laboratory stage, compared to the traditional process of LIFT, its nozzle free characteristics, pixel-based transfer method, make it have high production efficiency, universality of materials, and compatibility with Computer numerical control (CNC) machine tools. In this review, the fundamental principle of LIFT is introduced and the great potential of LIFT in many fields is presented and analyzed, including Three-dimensional (3D) bioprinting, industrial manufacturing, energy storage material manufacturing, new-type energy and so on. The conclusion is that if the application of LIFT in the manufacturing field can be achieved, the efficiency and flexibility of modern digital production will be greatly improved. The LIFT method has great development prospects in the manufacturing field.

Innovative Fabrication of Metal Alloy Structures via Laser-Induced Forward Transfer on Flexible Substrates.

Laser-induced forward transfer is a contactless, nozzle free process which enables accurate, precise and fast development of 3D structures. However, a number of shortcomings such as shockwave generation, poor adhesion to receiver substrates and uniform depositions limit LIFT to be utilized. Therefore, this research tends to put forward easy and effective solutions for successful mitigation of the LIFT limitations. Receiver surface modifications and low-pressure conditions are introduced through laser surface texturing (LST) and a vacuum pump. A number of textures and orientations are investigated for determining the optimal copper (Cu) deposition. Furthermore, utilization of the same laser system for LST enables the manufacturing process cost and time effective. In addition to Cu depositions, additive layers of silver (Ag) and platinum (Pt) are deposited. Finally, Ag and Pt micropillars are fabricated on their respective additive layers leading to formation of Cu-Ag and Cu-Pt alloys structure. Subsequently, electrical and material characterizations are made to validate for potential applications. Experimental evidence shows greater adhesion with electrical properties for LST-based LIFT in low pressure conditions. Finally, an energy analysis is performed based on theoretical and finite element methods (FEM) to gain greater insights into mechanics of the LIFT process.

Bioprinting with 3-µm laser pulses

Laser-Induced Forward Transfer (LIFT) technology has now found its wide application in the field of bioprinting. Laser bioprinting allows the spatial transfer of living micro-objects (cells, microorganisms) in a gel medium using the energy of a laser pulse. Typically, to effectively absorb laser pulse energy, a thin metal layer is deposited on the donor substrate. The disadvantages of this approach are the appearance of cytotoxic metal nanoparticles during laser bioprinting and the need for continuous movement of the donor substrate. The article proposes a method that allows moving to absorption film-free bioprinting using Q-switched Er:YAG nanosecond laser operating at a wavelength of 2.94 µm. This wavelength is effectively absorbed in a top ten-micron hydrogel layer, allowing for a cleaner (without nanoparticles from absorbing layer) and simpler (without the need to constantly move the donor substrate from pulse to pulse) laser bioprinting process. Using strain Escherichia coli as an example, the suitability of the proposed method for successful laser bioprinting is demonstrated. A model describing in detail the processes occurring in the hydrogel layer is presented.

Laser-Induced Printing of Next Generation Silicon-Graphite Anodes for the Development of Advanced Lithium-Ion Batteries

The expansion of renewable causing a rising demand for affordable and improved energy storage systems. Lithium-ion batteries (LIB) are one of the most promising technologies for this achievement, with further improvements to be made in terms of new materials and an advanced electrode architecture. As a new generation electrode material to be included in LIB, silicon is in the focus of the today’s investigations. Silicon offers one order of magnitude higher theoretical specific capacity (3579 mAh/g) compared to the state-of-the-art material graphite (372 mAh/g). However, during lithiation of silicon a volume expansion of up to 300 % takes place. Due to the huge volume expansion tremendous mechanical degradation of the anode occurs, resulting in a drop in capacity and a shorten lifetime.Laser induced forward transfer (LIFT) is applied in this study as printing technology to develop enhanced silicon-graphite electrode compositions and electrode architectures. LIFT was performed using a pulsed nanosecond UV-laser with a maximum power of 10 W and repetitions rate of up to 30 kHz. For the LIFT process of anodes, polyacrylic acid (PAA) is used as binder, in contrast to the polyvinylidene fluoride (PVDF) binder commonly used for LIFT assisted printing of electrodes. PAA is a more appropriate binder for silicon-containing anodes than PVDF. In addition, also a customized architecture using subtractive and additive laser process techniques is introduced for an increase in lifetime of batteries containing silicon-based electrodes. For this purpose, graphite electrodes were structured with an ultrashort pulse laser with pattern widths of 100 µm. Subsequently, silicon rich slurry was printed into the patterns to increase the areal capacity. The as-prepared electrodes have spatially separated graphite and silicon regions. The respective electrodes were electrochemically cycled in half-cells and charged at different C-rates up to 5C to investigate their lithiation capability. After the rate capability analysis, the cells were cycled at C/2 to investigate the long-term degradation. The cells with the printed electrodes were cycled for more than 450 cycles with a capacity fade of 5 %. At their end-of-life, the cells were analyzed post-mortem. Finally, full-cells were assembled with cathodes containing NMC 622 as the active cathode material. Subsequently to the cell priming a lifetime analysis was performed at a C-rate of C/2 and cycle stability as well as lithium loss during cycling were evaluated.

Tilting behaviors of metal microjet in laser-induced forward transfer

Abstract Laser-induced forward transfer (LIFT) is proposed as a highly efficient and high-resolution printing technique. Tilting of the microjet in the LIFT process affects the deposition deviation, lowing the printing resolution. We investigate the tilting behaviors of the metal microjet in the nanosecond LIFT process based on high-speed observation. Experiments were conducted on the copper film under different laser fluences. Observations based on the pump-probe method were performed to capture the ejection behavior of microjets. We find that the tilting direction is isotropic and the tilting angle follows Gaussian distribution. The tilting behavior originates from the disturbance of residual stress within the film during jet generation because the statistical results of the tilting angle hardly vary with the propagation time. In addition, the tilting angle is found to decrease linearly with the laser fluence due to the ejection velocity increasing at a higher rate than the lateral velocity. The lateral offset of the tilting microjet at different flight distances matches well with the position deviations, verifying the tilting behavior of the microjet. This study provides essential comprehension of the tilting behavior of metal microjet in the LIFT process.

Elucidation of the visualization process and its influencing factors for the preparation of microcircuits based on arc-beam laser-induced forward transfer

Arc beam laser-induced forward transfer (AB-LIFT) based on an arc beam is a promising micro additive manufacturing process to efficiently prepare high-performance metal microcircuits by transferring metal microdroplets. Therefore, elucidating the transfer mechanism of arc-beam-induced microdroplets is crucial to controlling the printing process. In this paper, a dark-field imaging system is developed to visually analyze the transfer process of metal microdroplets, and the injection mechanism of Gaussian and arc-beam laser-induced forward transfer is analyzed. Meanwhile, by studying the deposition behavior of laser-induced forward transfer micro drops with an arc beam at a single pulse energy, it is concluded that the factors affecting the laser-induced forward transfer with an arc beam mainly include the center angle and diameter of the arc beam. Then the effects of the center angle and diameter of the arc beam and the laser parameters on the preparation of microcircuits by AB-LIFT are systematically investigated, and a set of process methods for the effective preparation of high-performance microcircuits is proposed.

Femtosecond laser printing-assisted etching tailored hard and brittle micro-convex surface.

We report a femtosecond laser print-assisted dry etching technology for high-efficiency, high-quality, and tailored fabricating of a micro-convex surface (MCS) on hard and brittle materials. Liquid ultraviolet curing adhesive (UVCA) was transferred from a donor substrate to a receiving substrate by femtosecond laser-induced forward transfer, and the transferred microdroplet spontaneously has a smooth surface under the action of surface tension. And then an MCS with a high-quality surface was formed on hard and brittle materials by UV curing and dry etching. The effects of laser parameters and receiving substrate surface free energy on MCS morphology were investigated. According to the variation of the numerical aperture, the two methods to change the morphology of the MCS were divided into independent/joint regulation of diameter and height. We showed that a hexagonal array containing a variety of MCS morphologies can be fabricated on a fused silica by setting the appropriate parameters. And the fabrication time of an MCS in a large-area array was only 1.1s.